Holley Power Valve

[Bill S.]

Looking for the symptoms of a bad power valve in my holley carb. If it fails will it cause the carb to backfire and the plugs to be wet with fuel? Thanks Bill

[Wayne W.]

Re: Holley Power Valve

Probably not. The back fire would most likely be the cause of the bad power valve. Would run rich and be hard to adjust idle.

[JAT]

Re: Holley Power Valve

I have been running Holley double pumpers on my 68 and 70 since 1973 and this is how I can usually tell if a primary power valve needs replacing. With the engine running put your finger over the vertical vent tube. If the engine dies right away, the primary power valve is bad. Consquently, if it isn't bad the car will idle for a short period with the vent tube blocked.I could also usually also tell just by the performance of the engine, little bit of black smoke from the exhaust, and the idle problems. I have found them at Auto Zone for about $6.00.I always keep spare power valves and bowl and metering block gaskets on hand and don't leave home without them if going out of town, course I carry a spare fuel pump also. Have been guilty of carring a water pump. Isn't that what those storage compartments are for?

[Bill Baird]

Re: Holley Power Valve

I agree with Wayne. The backfire probably did in the power valve. If you've lost the primary power valve, then the car won't idle worth a damn (Hell, the car won't even stay running without a bit of throttle) and you'll run severely rich. I once lost a primary power valve on the highway on the way to the Bloomington Gold show, and I used a tank of gas in 15 minutes! Ever since then, I carry the necessary spare carb parts on any long trip.


Now if your carb also has a power valve in the secondaries, and it goes bad, then the symptoms will usually be a little less severe. a marginally bad idle that just comes out of nowhere. While that can be caused by a variety of things, I've kind of learned to "feel" when the secondary power valve is at fault.


I wonder if those Speed Demon carbs I've seen in the Summit catalogs are any better at this kind of thing than the Holleys? They wouldn't be original, but they would do for some street driving. Has anybody tried one these yet and wish to comment?


Bill Baird

[Clem Z.]

Re: Holley Power Valve

the after market companys sell a kit that consist of a small spring and a ball bearing that is installed in the PV vacuum port that prevents backfires from doing in the PV. all new holley carbs come with this feature. i think holley also sells this item in their catalog.